Virtually every consumer product device on the market has some form of input mechanism that allows a user to interact with the device. One of the most common input mechanisms is the button, which when pressed by a user causes the device to change a state associated with the button. The button may take many forms, from a mechanical push button, such as a rubber knob commonly found on TV remote controls and calculators, to a virtual button, such as a graphical user interface input area displayed on a flat and/or rigid touch-sensitive surface commonly found on ATMs and some handheld computing devices.
Irrespective of the form, the button is usually associated with two states—“pressed” or “not pressed”. Pressing or selecting a button changes the “not pressed” state to “pressed”, causing the “pressed” state to be activated. Releasing the button changes the “pressed” state back to “not pressed”, causing the “pressed” state to be deactivated. In this sense, the button allows a user to define the state of input into the device.
For example, when a device is powered off and a user presses the power button, the button press activates the power button's “pressed” state, which triggers the device to power on. When the user releases the button, the button release deactivates the “pressed” state, usually to no effect. In a different example, when a user presses a horn on a car (which can be considered a large button), the horn press activates the horn's “pressed” state, triggering the car to sound the horn. When the user releases the horn, the horn release deactivates the “pressed” state, triggering the car to stop sounding the horn.
The mechanism behind the operation of many buttons is a force sensor. When a user presses a button, a force sensor detects the force being applied to the button from the user's finger, hand or other object. When the output of the sensor indicates that the force exceeds a threshold amount (e.g., a strong enough press of the user's finger to indicate the user is intending to press the button), the “pressed” state of the button is activated, triggering an action to be taken by the device due to the button being pressed.
Thus, in order for the button to work properly, it is important that the button's sensor output be interpreted correctly to indicate that the button has been pressed or released. An incorrect interpretation of the button's sensor output can result in a phantom button press or release, which can trigger an unintended action with potentially damaging consequences.